The present invention relates to digital communications, and more particularly, to methods and systems for transporting time division multiplex (TDM) data via packet-based networks.
TDM data may consist of Constant Bit Rate (CBR) data as well as non-CBR data. CBR data includes real-time data such as voice, video or professional, studio quality (i.e., program) audio. Typically, constant bit rate (CBR) data is formatted into 64 kbps time-slots (TS) and TDM techniques are used to map the time-slots into T1 or E1 frames which are transported over the Public Switched Telephone Network (PSTN).
In one “real world” example of CBR data, the program audio produced in a studio must be relayed to a remote transmitter site for subsequent broadcast. In some cases, a studio-to-transmitter link (hereinafter referred to as STL) may be implemented with a T1 (or E1) digital circuit via the PSTN. In prior art, this digital circuit is typically implemented using expensive “nailed up” (i.e., dedicated) T1 lines. One way to reduce the cost of such an STL is to relay the professional quality audio data over an existing, general purpose packet based network such as the Internet. Other formats of CBR data that would normally be transmitted via a dedicated T1 line (e.g., MPEG, APT-X, Linear etc.) also could be advantageously transported via a packet based network. A unique “convergence layer,” i.e., a set of rules that defines how to encapsulate the T1/E1 data into the individual packets of the packet based network, must be specifically designed for each particular media type. Thus, each individual convergence layer is media-specific. Further, more generic types of data, such as voice, video, synchronous data, asynchronous data, etc., could also benefit by being transported over packet networks.
A disadvantage of prior art systems for encapsulating T1 or E1 TDM-based data into a packet based communications protocol is the requirement for unique convergence layers for each data type. Further, prior art techniques for encapsulating T1 or E1 data into a packet based protocol typically encapsulate all of the T1 overhead bits, as well as the payload data, which reduces the overall bandwidth efficiency.